Method and apparatus for determining a deviation between clock pulse devices

ABSTRACT

The invention relates to a method for synchronizing clock pulse devices. According to this method, an emission unit emits at least one narrow-band distant signal; clock pulse devices of receiving units are pre-synchronized by coupling the same to the source of one such distant signal; the emission unit emits a wide-band measured signal after a defined waiting time, and the receiving units receive said signal; and the receiving units correlate the wide-band measuring signal with a homogeneously modulated comparison signal, the receiving time of the wide-band measuring signal and the deviation in the synchronization of the clock pulse devices being determined and compensated on the basis of the correlation result.

BACKGROUND

The invention concerns a method for synchronization of clock pulsedevices, in particular for the purpose of a precise positiondetermination of an object in a radio-based positioning system.

Measurement methods which are based on the TDOA (“Time Difference ofArrival”) principle are known according to FIG. 1. A transponder T to belocalized thereby repeatedly emits a transponder signal T_(S) at certainpoints in time. This transponder signal T_(S) is then received atmultiple M base stations whose positions are fixed and known. The M basestations BS₁, BS₂, . . . , BS_(M) possess means to precisely determinethe arrival point in time of the transponder signal T_(S). Forcalculation of the position of the transponder T, the delay differencet₁−t₂, t₁−t₃ or t₂−t₃ of the transponder signal T_(S) between thetransponder T and at least two base stations BS₁ and BS_(M) isevaluated. In order to be able to precisely measure the delaydifferences, it is necessary to let the clock pulse sources of the basestations BS to run synchronously among one another. For this, either avery elaborate real-time capable background network or highly-precise,long-term stable clocks is required.

Coded signals are typically used as a transponder signal T_(S), and thedetermination of the arrival point in time of the signal T_(S) at thebase stations BS ensues via a correlation with a signal known to thebase station BS. Such a correlation is, however, verycomputation-intensive for broadband and radio-frequency signals. If thetransponder T and base station BS participating in a measurement are notsynchronized, this correlation must ensue continuously and in areal-time capable manner in each base station. This is, at present, onlyeconomically realizable for a limited bandwidth with digital circuits.

A method for synchronization of a transmitter station and a receiverstation that communicate with one another via a radio interface is knownfrom German Patent Document DE 101 57 931 A1 (“DE '931”), that disclosesa system in which, in the transmitter station, a transmission signal isgenerated with a signal source and emitted via the radio interface and acorresponding reception signal is received in the receiver station bythe radio interface and is evaluated using a receiver signal sourcesignal from a signal source on the receiver side that is adapted to thesender-side signal source.

For up-to-date adaptation of the synchronization between a transmissionsignal and a reception signal, similar modulations are applied to thetransmission signal and the reception signal and both are intermixedwith one another. The mixed signal is subsequently analyzed with regardto a frequency detuning.

SUMMARY

The invention is based on the object to provide a method and/or anarrangement in which signals can be synchronized among one another suchthat a precise position determination of a radio station is ensured viathe calculation of delay differences of these signals from one radiostation and a plurality of others.

The object is achieved via a method for synchronizing clock pulsedevices, comprising: emitting, by a transmitter unit, at least onenarrow-band pre-signal; pre-synchronizing clock pulse devices ofreceiver units to a source of the pre-signal via a coupling to such apre-signal; emitting, by the transmitter unit, a broadband measurementsignal after a specific wait time and receiving, by the receiver units,this signal; and correlating, by the receiver units, the broadbandmeasurement signal with a similarly modulated comparison signal and,based on a correlation result, determining a reception point in time ofthe broadband measurement signal and a deviation of the synchronizationof the clock pulse devices and this is compensated.

As a solution, according to an embodiment of the invention, a method forsynchronization of clock pulse devices is proposed in which:

-   -   a transmitter unit emits at least one narrow-band pre-signal,    -   clock pulse devices are pre-synchronized to the source of the        pre-signal via a coupling to such a pre-signal,    -   the transmitter unit emits a broadband signal after a specific        wait time and the receiver units receive this signal,    -   the receiver units correlate the broadband measurement signal        with a similarly modulated comparison signal and, based on the        correlation result, the deviation of the synchronization of the        clock pulse devices is determined and compensated.

The clock pulse devices can also be designated as clocks. If asynchronicity of the clocks exists, a majority of the computation effortfor determination of the arrival point in time of a signal whoseoriginal position is not known can be assumed by simple analog circuitelements. Since the synchronization ensues via radio communications,advantageously, no network cabling among the transmitter units andreceiver units is necessary.

Base stations can be used as receiver units and transponders whoseposition is measured can be used as transmitter units. The transpondercan be realized merely as a transmitter unit which itself receives nosignal. Advantageously, only the base stations are synchronized amongone another since these normally also have the possibility to receiveclocked signals.

For position determination of the transmitter unit, according to anembodiment of the invention, a method is provided in which

-   -   a method for synchronization of clock pulse devices is executed        as above, and    -   the arrival point in time of the broadband measurement signal is        calculated based on the correlation result and the position of        the transmitter unit can be determined via a comparison of the        delays of the measurement signal received by the receiver units        and transmitted by the transmitter unit.

The method can be expanded in that a reference station with its ownclock pulse source (the position of which reference station is known)emits a reference signal. This is received by the receiver units and theclock pulse devices of the receiver units synchronized on this referencesignal. The reference station is advantageously fashioned as atransmitter unit in the form of a reference transponder.

However, not only the receiver units but, rather advantageously, alsothe transmitter unit, can be synchronized from the referencetransponder. For this, the transmitter unit must also be expanded as areceiver unit. Advantageously, this results in the base stations knowingat which point in time each transmitter unit transmits due to thecoupling between the reference transponder and the transmitter unit or,respectively, transponder. The initial type of cited correlation in realtime is therewith no longer necessary. The base stations can naturallylikewise also serve as transmitter units, such that they can communicateamong one another and, if applicable, pre-synchronize among one another.

A radio communication arrangement can form the basis of and embodimentof the inventive method, which radio communication arrangementcomprises:

-   -   a transmitter unit and a plurality of transmitter and receiver        units which respectively comprise a clock pulse device, a signal        source and a radio interface,    -   a reference station whose position is known and which comprises        a clock pulse device and a signal source via which reference        signals of a predeterminable clock can be generated, whereby,    -   a synchronization of the clock pulse devices of the transmitter        and receiver units can be achieved in that the delay differences        of the reference signals that are to be expected are known to        the plurality of transmitter and receiver units due to the known        position of the reference station, and thus    -   the clock pulse devices of the transmitter and receiver units        can be offset among one another in a uniform clocked state using        a coupling to the clock pulses of the reference signals.

It is advantageous when the radio communication arrangement is realizedas a position measurement system or, respectively, as a radio-basedpositioning system in that distances between the transmitter andreceiver units are measured. The position measurement system isadvantageously to be used for the measurements of large distances,whereby in this case naturally the transmitter and receiver unitsexhibit a corresponding distance relative to one another.

DESCRIPTION OF THE DRAWINGS

Advantageous developments of the invention result from the followingexemplary embodiments illustrated in the drawings.

FIG. 1 is a block diagram illustrating a known radio communicationarrangement with base stations and a transponder;

FIG. 2 is a block diagram illustrating a radio communication arrangementwith base stations, a transponder and a reference transponder;

FIG. 3 is a timing diagram illustrating an embodiment forsynchronization of clock pulse devices and for position determination ofa transmitter unit with successions of pre-signals and measurementsignals; and

FIG. 4 is a block diagram illustrating a preferred design of transmitterand receiver units.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows how a reference transponder T_(Ref) is prepared at a knownposition. The base stations BS_(1-M) are advantageously synchronizedamong one another with the aid of the arrangements and method describedin DE '931. For the devices which are used in this method from DE '931,reference is made to FIG. 4. In this method, a transmitter station or,respectively, transponder SE, and a receiver station or, respectively,base station BS, are assumed to communicate with one another via aninterface. In this arrangement, a transmission signal sig₁ is generatedin the transmitter station with a signal source Sgen₁, and is emittedvia the interface. In the receiver station BS, a corresponding receptionsignal esig₁ is received by the interface and is evaluated using areceiver signal source signal sig₂ from a receiver-side signal sourceSgen₂ adapted to the transmitter-side signal source Sgen₁.

The method is characterized in that a similar modulation is applied bothto the transmission signal sig₁ and to the receiver signal source signalesig₁, and the reception signal received in the receiver station BS ismixed with the receiver signal source signal sig₂ into a mix signalsigmix, and the mix signal is analyzed. Naturally the base stations BSmust also serve as transmitter units for such a communication. After thebase stations BS are at least roughly synchronized with one another, thevalues of the signal delay differences |t₄−t₅| between the referencetransponder T_(ref) and a plurality of base stations BS_(1-M) serve tosynchronize the base stations more exactly among one another since theposition of the reference transponder, and thus also the signal delaydifferences |t₄−t₅| to be expected, are known. The position of thetransponder T can now be precisely determined via the synchronized basestations BS_(1-M) in that delay differences |t₁−t₂| or |t₂−t₃| or|t₃−t₁| of the signal emitted by the transponder T to the base stationsBS are evaluated. A triangulation or trilateration method can thereby beused for the position determination of the transponder T.

The reference transponder T_(ref) comprises at least one signal sourceand a radio interface. It is also provided with a clock pulse sourcewhich clocks the signal source. The reference transponder can thus serveas a clock master for all remaining transmitter and receiver units sothat the signals originating from these units are synchronized among oneanother. In order to be able to achieve an even higher precision, aplurality of reference transponders T_(ref) can naturally be used.

A development of the invention exists in that the transponder T to belocalized (thus not only the base stations BS_(M)) is also synchronizedto a specific clock master, for example, the reference transponder. Thetransponder signal should thereby be a coded signal, such that at whichpoint in time (relative to the clock of the clock master) eachtransponder transmits is known to all base stations per se or via aradio data transmission. The very elaborate correlation with thisbroadband measurement signal no longer has to ensue in a real-timecapable manner, but rather can be implemented offline after a datarecording. The computational effort or, respectively, the bandwidth ofthe signal to be evaluated can also be reduced by orders of magnitudevia mixing processes as they are described in DE '931 and via evaluationof the mix signal.

FIG. 3 is a timing diagram showing the course of a series of signals forsynchronization of radio stations. In this situation, there is no longeronly one special clock master; rather, every transponder, regardless ofwhether it is a reference transponder or a transponder to be localized,takes on this function as needed. The localization process thereby runsas follows:

Each transponder that would like to initialize a measurement emits aninitially very narrow-band pre-signal V1, whereby in FIG. 3, thefrequency spectrum or, respectively, the frequency axis is identifiedwith f. In the normal case, all base stations implement a real-timecorrelation; this should detect this pre-signal V1. Each base station BSthat detects such a pre-signal V1 synchronizes to the source of thispre-signal V1 according to the method from DE '931. After a specificwait time T_(w) known to the base station, the transponder T then sendsthe actual broadband measurement signal V3.

The pre-signal V1 advantageously also comprises some further informationsuch as identification number of the transponder and specificationsabout the wait time T_(w) between pre-signal V1 and measurement signalV3 or also the time duration until the emission of the next signal. In awholly unsynchronized state, the pre-signal V1 is advantageouslyrepeated slightly time-shifted at least once to increase the assuranceof detection of a pre-signal V2. The repetition signal is designatedwith V2. The wait time T_(r) should be selected such that it correspondsto approximately half of the modulation duration T of the pre-signal.

A preferred embodiment of the invention exists in that not only arevarious base stations synchronized to the respective active transponderswith the pre-signals V1 and V2, but rather, a reference transponder at aknown position also receives the pre-signals V1 and V2 and likewisesynchronizes to these pre-signals using these. After a specific waittime T_(w), the transponder then sends the actual broadband measurementsignal V3.

The reference transponder likewise sends a similarly-modulated broadbandreference measurement signal RV3 offset by a very small time shiftrelative to T_(w). The time offset is selected such that it isdistinctly smaller than the length of the broadband measurement signalsV3. In the arrangement shown in FIG. 4, both the broadband measurementsignal V3 and the broadband reference measurement signal RV3 are thensimultaneously mixed with sig2 in the base stations BS. Two signalcomponents—one originating from the transponder and one originating fromthe reference transponder—are now found in the signal sigmix, usingwhich two signal components the arrival times of and the time differencebetween the transponder signal and the reference transponder signal RV3can be determined very exactly in each base station BS. The position ofthe transponder T can then be determined very well based on the arrivaltimes or, respectively, time differences.

An alternative would be visible in that all participants aresynchronized not to a transponder but rather to a reference transponder.The reference transponder would then, for its part, have to provide (viasending of identification signals (addressing specific transponderaddresses)) that no more than one transponder emits a measurement signalat the same time.

It is preferred that the position of the transponder to be localized iscalculated after various base stations BS have received both the signalsof the reference transponder described with respect to FIG. 2 and of thetransponder to be localized.

FIG. 4 shows how a transmitter unit SE sends a transmission signal sig1via a signal generator Sgen₁, which transmission signal sig₁ is radiatedvia the transmission antenna A_(T) to the base station BS. The form ofthe signal sig₁ is permanently preset. It is advantageous when sig₁ is afrequency-modulated signal (for example a FMCW signal). The frequencymodulation can ensue linearly, step-by-step, or in digital stages. Suchsignals are advantageously used as they are also described in DE '931.The base station BS is uniformly designed in large parts. A signal sig₂is generated here in the same manner as in the transmitter unit SE.

The signal received via the antenna A_(R), which signal was previouslygenerated by the transmitter unit SE, is mixed with sig₂ with a mixerMIX. The mix signal sigmix is supplied to an evaluation and control unitASE that evaluates the mix signal sigmix.

A further embodiment is to likewise expand the unit previouslydesignated as a transponder with similar receiver mechanism like thebase station. After the base station is synchronized (as alreadydescribed before) using the pre-signals V1 and V2 and has received theactual measurement signal and calculated the arrival point in time andthe exact synchronization parameters according to DE '931, the basestation now, for its part, generates a response signal (based on thearrival point in time and the synchronization parameters) that is nowsent to the transponder after a stipulated time span and is received bythis transponder and, as provided before, the arrival point in time ofthe response signal is calculated. The response signal has a modulationnearly identical to sig₁ and is mixed (as described for the base stationor in DE '931) with a modulated signal like sig₁ (advantageously, likeV3 in FIG. 3), and the arrival point in time is calculated from theremaining signal.

The signal delay, and thus the radio channel length, and thus theseparation between base station and transponder, can then be calculatedfrom the time difference between query and response under considerationof the stipulated time span. This advantageously occurs using agenerally known rough time of flight (RTOF) method. In typical systemswithout the synchronization according to the method, this method breaksdown in all cases in that two spatially separate systems cannot agreeupon exact time spans, in particular not on longer time spans, sincetheir clock bases are not identical. However, a highly-precisecompensation of the clocks can ensue via the synchronization.

Since here the actual measurement information (namely, the separationvalue) is acquired in the transponder, it makes sense to exchange thenomenclature and to name the transponder so expanded as the base stationand the base station the transponder. In many applications, it can alsobe reasonable to hold the expanded transponder stationary and to operatethe base station mobile. An advantage of this arrangement is that thedirect distances between two stations are measured and not delaydifferences (thus delays of 3 participants) as in the time difference ofarrival (TDOA) principle. This direct delay measurement immanentlyenables a highest-possible flexibility—for example, even this exchangecapability of the functions—and harmonizes in a particular manner withtypical communication systems in which the communication also runsnormally between only two participants. This method is thereforeparticularly well suited for apparatus in self-organizing radio networksor in sensor networks.

It is also noted that the cited RTOF arrangement, according to theembodiment, is also very well suited for a transponder or, respectively,RFID (radio frequency identification) systems, since with them, thedelay between a base station and a transponder can be determined. If thetransponder additionally transmits an identification code, it is thus aclearly-improved identification system since not only the identity butrather also the distance of the object with the specific identity can bedetermined. This supplementary information can be used veryadvantageously in the field of automation technology, logistics, or inaccess or security systems.

For the purposes of promoting an understanding of the principles of theinvention, reference has been made to the preferred embodimentsillustrated in the drawings, and specific language has been used todescribe these embodiments. However, no limitation of the scope of theinvention is intended by this specific language, and the inventionshould be construed to encompass all embodiments that would normallyoccur to one of ordinary skill in the art.

The present invention may be described in terms of functional blockcomponents and various processing steps. Such functional blocks may berealized by any number of hardware and/or software components configuredto perform the specified functions. For example, the present inventionmay employ various integrated circuit components, e.g., memory elements,processing elements, logic elements, look-up tables, and the like, whichmay carry out a variety of functions under the control of one or moremicroprocessors or other control devices. Similarly, where the elementsof the present invention are implemented using software programming orsoftware elements the invention may be implemented with any programmingor scripting language such as C, C++, Java, assembler, or the like, withthe various algorithms being implemented with any combination of datastructures, objects, processes, routines or other programming elements.Furthermore, the present invention could employ any number ofconventional techniques for electronics configuration, signal processingand/or control, data processing and the like. The word mechanism is usedbroadly and is not limited to mechanical or physical embodiments, butcan include software routines in conjunction with processors, etc.

The particular implementations shown and described herein areillustrative examples of the invention and are not intended to otherwiselimit the scope of the invention in any way. For the sake of brevity,conventional electronics, control systems, software development andother functional aspects of the systems (and components of theindividual operating components of the systems) may not be described indetail. Furthermore, the connecting lines, or connectors shown in thevarious figures presented are intended to represent exemplary functionalrelationships and/or physical or logical couplings between the variouselements. It should be noted that many alternative or additionalfunctional relationships, physical connections or logical connectionsmay be present in a practical device. Moreover, no item or component isessential to the practice of the invention unless the element isspecifically described as “essential” or “critical”. Numerousmodifications and adaptations will be readily apparent to those skilledin this art without departing from the spirit and scope of the presentinvention.

1. A method for determining a deviation between clock pulse devices, comprising: emitting, by a transmitter unit, at least one narrow-band pre-signal using a clock pulse device; pre-synchronizing clock pulse devices of receiver units to a source of the pre-signal via a coupling to such a pre-signal; emitting, by the transmitter unit, a broadband measurement signal after a specific wait time and receiving, by the receiver units, this broadband measurement signal; and correlating, by the receiver units, the broadband measurement signal with a similarly modulated comparison signal and, based on a correlation result, determining a reception point in time of the broadband measurement signal and determining a deviation of the synchronization of the clock pulse devices.
 2. The method according to claim 1, farther comprising: waiting for a specific wait time, and then emitting a further narrowband pre-signal that follows after the emission of a first pre-signal to increase detection assurance, to which narrowband pre-signal the clock pulse devices couple.
 3. The method according to claim 2, wherein a time span between the first pre-signal and the further pre-signal corresponds to half of a modulation duration of the first pre-signal.
 4. The method according to claim 2, wherein the at least one pre-signal comprises specifications about the wait time until the emission of the broadband measurement signal.
 5. The method according to claim 1, wherein the pre-signal comprises specifications about a wait time until the emission of the further pre-signal.
 6. The method according to claim 1, wherein the transmitter unit is realized as a transponder and the receiver units are realized as base stations.
 7. The method according to claim 1, further comprising: providing an identification number of the transmitter unit within the at least one pre-signal.
 8. The method according to claim 1, further comprising: providing the transmitter unit and receiver units in a radio-based positioning system.
 9. The method according to claim 1, further comprising: utilizing the method for determining a deviation between clock pulses in a system for determining a position of a transmitter unit; calculating an arrival point in time of the broadband measurement signal based on the correlation result and the position of the transmitter unit that can be determined via a comparison of the delays of the measurement signal received by the receiver units and transmitted by the transmitter unit.
 10. The method according to claim 9, wherein the comparison of the delays is executed using a TDOA method.
 11. The method according to claim 9, further comprising: emitting a reference signal with a reference station provided with its own clock source, the position of which reference station is known; receiving this reference signal by the receiver units; and synchronizing the clock pulse devices of the receiver units on this reference signal.
 12. The method according to claim 1, further comprising: receiving, by the reference station, the pre-signals of the transmitter unit; synchronizing, by the reference station, these pre-signals; emitting, by the transmitter unit, the broadband measurement signal after the specific wait time; emitting, by the reference station, a similarly modulated broadband reference measurement signal offset by a slight time shift relative to the determined wait time, selecting the time offset such that it is distinctly smaller than a length of the broadband measurement signals; mixing both the broadband measurement signal and the broadband reference measurement signal with a similarly modulated comparison signal into a mix signal in the receiver units the arrival points in time of the measurement signals; and b) the time difference between the measurement signals using the signal components of the transmitter unit and of the reference station comprised in the correlated mix signal; and determining a position of the transmitter unit based on at least one of arrival points in time and time difference.
 13. The method according to claim 8, wherein the transmitter unit is suited for reception of signals, flirt her comprising: after the synchronization of the receiver units via the pre-signals and via the measurement signal; generating, by the receiver units a response signal based on the arrival point in time of the measurement signal; transmitting this response signal to the transmitter unit after a stipulated wait time; receiving this signal, and calculating an arrival point in time of the response signal is calculated there; and calculating, based on the stipulated wait time, the signal delay and thus the separation between the transmitter unit and the receiver.
 14. The method according to claim 9, farther comprising: after the synchronization of the receiver units via the pre-signals and via the measurement signal; generating, by the receiver units a response signal based on the arrival point in time of the measurement signal; transmitting this response signal to the transmitter unit after a stipulated wait time; receiving this signal, and calculating an arrival point in time of the response signal is calculated there; and calculating, based on the stipulated wait time, the signal delay and thus the separation between the transmitter unit and the receiver.
 15. The method according to claim 9, further comprising: utilizing the transmitter unit and receiver unit for position determination of a transmitter unit in a radio-based positioning system.
 16. The method according to claim 1, further comprising: determining and compensating the deviation of the synchronization of the clock pulse devices.
 17. A system for determining a deviation of clock pulse devices, the system comprising: a transmitter unit configured to emit at least one narrow-band pre-signal, and then to emit a broadband measurement signal after a specific wait time, the transmitter unit configured to use a clock pulse device; a plurality of receiver units, each receiver unit comprising: pre-synchronization means for pre-synchronizing the clock pulse devices to the source of the pre-signal via a coupling to the pre-signal; receiving means for receiving the broadband measurement signal; correlation means for correlating the broadband measurement signal with a similarly modulated comparison signal; and determination means for determining, based on the correlation result, the reception point in time of the broadband measurement signal and the deviation of the synchronization of the clock pulse devices.
 18. A method at a receiver unit for determining a deviation between clock pulse device, the method comprising: receiving at least one narrow-band pre-signal transmitted by a transmitter unit, the transmitter unit using a clock pulse device; pre-synchronizing a clock pulse device of the receiver unit to the source of the pre-signal via a coupling to the pre-signal; receiving a broadband measurement signal transmitted by the transmitter unit after a specific wait time; and correlating the broadband measurement signal with a similarly modulated comparison signal and, based on the correlation result, determining the reception point in time of the broadband measurement signal and the deviation of the synchronization of the clock pulse devices.
 19. A receiver device for determining a deviation of clock pulse devices, the receiver device comprising: receiving means for receiving at least one narrow-band pre-signal transmitted by a transmitter unit, and for receiving a broadband measurement signal that has been transmitted by the transmitter unit after a specific wait time, wherein the transmitter unit uses a clock pulse device; pre-synchronization means for pre-synchronizing the clock pulse devices of the receiver device to the source of the pre-signal via a coupling to the pre-signal; correlation means for correlating the broadband measurement signal with a similarly modulated comparison signal; and determination means for determining, based on the correlation result, the reception point in time of the broadband measurement signal and the deviation of the synchronization of the clock pulse devices. 